1. Field of the Invention
The present invention relates to a fuel cell system which can start operating in low temperature conditions and a control method of the fuel cell system.
2. Description of the Related Art
For instance, a PEM (Proton Exchange Membrane) fuel cell using a solid polymer as an electrolyte membrane is generally employed for a fuel cell stack in a fuel cell electric vehicle. This kind of fuel cell stack is a stack of plural cells each of which is formed by a membrane electrode assembly (MEA) sandwiched between a pair of separators. Moreover, the membrane electrode assembly is formed by an electrolyte membrane whose both sides are sandwiched between an anode electrode and a cathode electrode. Thus, hydrogen and air (oxygen) are respectively introduced to the anode and the cathode electrodes of the fuel cell. Then, electric power and water is generated by electrochemical reaction between the hydrogen and the oxygen.
The water is mainly generated in the cathode while the fuel cell is operating. However, the water generated in the cathode infiltrates to the anode through the electrolyte membrane provided between the cathode and the anode. Accordingly, the water remains in pipes inside and outside the fuel cell in the fuel cell system when the fuel cell stops generating power. As a result, in a case of using the fuel cell under low temperature conditions such as in cold climate regions or in winter, when the fuel cell stops generating power with the water left in the pipes, the water might be frozen so as to cause the electrolyte membrane and so on to be damaged. Therefore, scavenging gas is introduced to the anode and the cathode to scavenge the water when the fuel cell stops generating power (refer to JP 2003-203665A).